1. Field of the Invention
The present invention relates to an optical pickup and optical device for use in a playback unit for an information recording medium such as an optical disc and more particularly to an optical pickup and optical device preferable for a compatible playback system for digital versatile disc (DVD) and compact disc-write once (CD-R).
2. Description of the Related Art
Currently, a DVD system has been proposed and marketed, and its prevalence has started, the DVD system having a higher density than an optical compact disc (CD) which had already prevailed as a consumer product. In DVD player as a playback unit of this system, compatible playback with CD is indispensable to avoid an overlapping of the devices and complexity of operation upon use. Likewise, the DVD player is also required to be compatible with the CD-R which can be played back by the CD player. A technology for playing back discs of various standards has been developed and further, simplification and reduction of cost for achieving it are problems to be solved.
For the aforementioned CD-R, a laser beam source having 780 nm band laser beam source different from 650 nm band for the DVD is required because reflectivity of an information recording medium has a high wave length dependency and therefore, an optical pickup containing a light source for two wave lengths (wavelengths) is necessary.
FIG. 1 is a schematic structure diagram of a conventional example of the optical pickup device. Referring to FIG. 1, a first laser beam source 51 is fixed on a first light receiving device (photodetector) substrate 50 and this first laser beam source 51 emits a light having a wave length (wavelength) of 650 nm. An emission light from the first laser beam source 51 passes through a first hologram device 52, and a light transmitting through a half mirror 53 is converged by an objective lens 54 and irradiated onto a disc 55 as an information recording medium. Alight reflected by the disc 55 is introduced to the hologram device 52 through the objective lens 54 and half mirror 53, and in the hologram device 52, the light is diffracted and divided. Then, xc2x1primary-order (xc2x1 1st-order) diffracted light is irradiated to the first light receiving device substrate 50. A second laser beam source 57 is fixed on a second light receiving device (photodetector) substrate 56 and the second laser beam source 57 emits a light having a wave length of 780 nm. An emission light from the second laser beam source 57 passes through a second hologram device 58 and is reflected by the half mirror 53 and converged by the objective lens 54 and irradiated to the disc 55 as an information recording medium. A light reflected by the disc 55 is introduced to the second hologram device 58 again through the objective lens 54 and half mirror 53. In the hologram device 58, the light is diffracted and divided and the xc2x1primary-order (xc2x1 1st-order) diffracted light is irradiated to the second light receiving device substrate 56.
FIG. 2 is a schematic structure diagram of other conventional example of the optical pickup device. In FIG. 2, a first laser beam source 60 and a second laser beam source 61 are disposed in the vicinity of each other. The first laser beam source 60 emits a light having a wave length of 650 nm and the second laser beam source 61 emits a light having a wave length of 780 nm. The emission lights from the first laser beam source 60 and second laser beam source 61 are emitted along substantially the same optical axis and reflected by a half mirror 62. The reflected lights are converged by an objective lens 63 and irradiated to a disc 64 as an information recording medium. Light reflected by the disc 64 passes through the objective lens 63, passes through the half mirror 62 and is irradiated to a light receiving device substrate 65.
However, because, in the former conventional example, optical paths from the laser beam sources 51, 57 to the half mirror 53 of the respective wave lengths are different from each other and the first laser beam source 51 and first light receiving device substrate 50 are disposed apart from the second laser beam source 57 and second light receiving device substrate 56, therefore, the optical pickup cannot be constructed in a compact configuration.
In the latter conventional example, the first laser beam source 60 and second laser beam source 61 are disposed in the vicinity of each other and although the optical paths thereof are the same, an optical path of incident light to the disc 64 is different from that of reflected light from the disc 64. Consequently, the first and second laser beam sources 60, 61 are disposed at a different position from that of the light receiving device substrate 65. Therefore, the optical pickup can be constructed in a compact configuration like the former example.
Here, such a structure in which the optical paths of the respective lights are the same and an optical path of an incident light to a disc coincides with that of a reflected light from the disc can be considered. In this case, a means for diffracting and dividing lights having different wave lengths is indispensable and further, if such a means is just disposed, usability of light from a laser beam source up to a light receiving device substrate via the disc drops considerably, so that practicability thereof is very low.
On the other hand, in a case for producing an optical device for the former conventional optical pickup, although as shown in FIG. 1, an optical device 70 in which a first laser beam source 51, a first light receiving device substrate 50 and a first hologram device 52 are integrally fixed in a casing(package) and an optical device 71 in which a second laser beam source 57, a second light receiving device substrate 56 and a second hologram 58 are integrally fixed in a casing(package) can be constructed in a compact configuration each, this example cannot make it possible to combine these optical devices to produce a compact single optical device.
In case for producing an optical device for the latter conventional optical pickup, although as shown in FIG. 2, an optical device 73 in which a first laser beam source 60 and a second laser beam source 61 are fixed in a casing(package) can be constructed, this example cannot make it possible to combine the first and second laser beam sources 60, 61, light receiving device substrate 65 and the like to produce a compact single optical device.
Accordingly, the present invention is achieved to solve the above problems, and therefore it is an object of the invention to provide an optical pickup and optical device in which light usability in a process from a laser beam source up to a light receiving device substrate hardly deteriorates unlike a conventional example and which can be constructed in a compact configuration.
To achieve the above object, according to a first aspect of the present invention, there is provided an optical pickup for irradiating light to an information recording medium and reading information by using a reflected light from the information recording medium, the optical pickup comprising: a first laser beam source having a first wave length; a second laser beam source having a second wave length; a first diffraction grating; a second diffraction grating provided on a face different from a face on which the first diffraction grating is provided; and a light receiving device substrate having a plurality of light receiving regions on the same plane, wherein the first laser beam source and the second laser beam source are disposed in the vicinity of each other, emission lights from the first laser beam source and the second laser beam source are emitted to the information recording medium along substantially the same optical axis and a reflected light from the information recording medium is returned along the optical axis; the first diffraction grating, the second diffraction grating and the light receiving device substrate are disposed in order substantially perpendicular to the optical axis; the first diffraction grating is substantially transparent for any one of the first wave length and the second wave length and diffracts the other wave length; and the second diffraction grating is substantially transparent for the other wave length while it diffracts the one wave length.
According to the present invention, a light emitted from the first laser beam source having a first wave length is diffracted by the second diffraction grating and this 0-order (0th-order) diffracted light is substantially transmitted through the first diffraction grating and then introduced toward the information recording medium. A reflected light from the information recording medium substantially is transmitted through the first diffraction grating and this light is diffracted by the second diffraction grating. Then, the xc2x1primary-order diffracted light is irradiated to the light receiving device substrate. A light emitted from the second laser beam source having a second wave length passes through the second diffraction grating and this passing light is diffracted by the first diffraction grating. The 0-order (0th-order) diffracted light is introduced toward the information recording medium and a reflected light from the information recording medium is diffracted by the first diffraction grating. The xc2x1primary-order diffracted light substantially is transmitted through the second diffraction grating and is irradiated to the light receiving device substrate. Thus, when a light having the first wave length and a light having the second wave length substantially pass through any one of the first and second diffraction gratings, they substantially are transmitted therethrough, and only when they pass through the other, they are diffracted. Consequently, light usability in a process from the first and second laser beam sources up to the light receiving device substrate is substantially the same as that of a conventional example. Further, because it is so constructed that the first laser beam source and second laser beam source are disposed in the vicinity of each other, emission lights from the first laser beam source and second laser beam source are emitted to the information recording medium along substantially the same optical axis and the reflected lights are returned along substantially the same optical axis as above-mentioned optical axis, the first laser beam source/second laser beam source and the light receiving device substrate can be disposed in the vicinity of each other, so that a compact optical pickup can be constructed.
To achieve the above object, according to a second aspect of the present invention, there is provided an optical pickup for irradiating light to an information recording medium and reading information by using a reflected light from the information recording medium, the optical pickup comprising: a first laser beam source having a first wave length and a linearly polarized light; a second laser beam source having a second wave length and a linearly polarized light substantially perpendicular to the polarized light of the first laser beam source; a first diffraction grating; a second diffraction grating provided on a face different from a face on which the first diffraction grating is provided; and a light receiving device substrate having a plurality of light receiving regions on the same plane, wherein the first laser beam source and the second laser beam source are disposed in the vicinity of each other, emission lights from the first laser beam source and the second laser beam source are emitted to the information recording medium along substantially the same optical axis and a reflected light from the information recording medium is returned along the optical axis; the first diffraction grating, the second diffraction grating and the light receiving device substrate are disposed in order substantially perpendicular to the optical axis; any one of the first diffraction grating and the second diffraction grating is substantially transparent for a linearly polarized light of any one of the first laser beam source and the second laser beam source and diffracts the other linearly polarized light; and the other one of the first diffraction grating and the second diffraction grating is substantially transparent for a wave length possessed by a laser beam source whose laser beam is diffracted by the first diffraction grating, of the first and second laser beam sources, and diffracts a wave length possessed by a laser beam source whose laser beam substantially is transmitted through the first diffraction grating, of the first and second laser beam sources.
According to the present invention, a light emitted from the first laser beam source, having the first wave length and linearly polarized light is diffracted by the second diffraction grating. Its 0-order diffracted light substantially is transmitted through the first diffraction grating and is introduced toward the information recording medium. A reflected light from the information recording medium substantially passes through the first diffraction grating and this light is diffracted by the second diffraction grating and the xc2x1primary-order diffracted light is irradiated to the light receiving device substrate. A light emitted from the second laser beam source, having the second wave length and a linearly(linear) polarized light perpendicular to the linearly(linear) polarized light from the first laser beam source is transmitted through the second diffraction grating. This passing light is diffracted by the first diffraction grating in a polarized state and the 0-order diffracted light is introduced toward the information recording medium. A reflected light from the information recording medium is diffracted by the first diffraction grating in a polarized state and its xc2x1primary-order diffracted light substantially is transmitted through the second diffraction grating and is irradiated to the light receiving device substrate. Thus, when a light having the first wave length and a light having the second wave length pass through any one of the first and second diffraction gratings, they substantially are transmitted therethrough, and only when they pass through the other, they are diffracted. Consequently, light usability in a process from the first and second laser beam sources up to the light receiving device substrate is substantially the same as that of a conventional example. Further, because it is so constructed that the first laser beam source and second laser beam source are disposed in the vicinity of each other, emission lights from the first laser beam source and second laser beam source are emitted to the information recording medium along substantially the same optical axis and the reflected lights are returned along substantially the same optical axis as above-mentioned optical axis, the first laser beam source/second laser beam source and the light receiving device substrate can be disposed in the vicinity of each other, so that a compact optical pickup can be constructed.
To achieve the above object, according to a third aspect of the present invention, there is provided an optical pickup for irradiating light to an information recording medium and reading information by using a reflected light from the information recording medium, the optical pickup comprising: a first laser beam source having a first wave length and a linearly polarized light; a second laser beam source having a second wave length and a linearly polarized light substantially the same as the first laser beam source; a wave length plate; a first diffraction grating; a second diffraction grating provided on a face different from a face on which the first diffraction grating is provided; and a light receiving device substrate having a plurality of light receiving regions on the same plane, wherein the first laser beam source and the second laser beam source are disposed in the vicinity of each other, emission lights from the first laser beam source and the second laser beam source are emitted to the information recording medium along substantially the same optical axis and a reflected light from the information recording medium is returned along the optical axis; the wave length plate, the first diffraction grating, the second diffraction grating and the light receiving device substrate are disposed in order from the information recording medium substantially perpendicular to the optical axis; any one of the first diffraction grating and the second diffraction grating is substantially transparent for linearly polarized lights of emission lights from the first laser beam source and the second laser beam source and diffracts a linearly polarized light substantially perpendicular to the linearly polarized lights from the first and second diffraction gratings, the other one of the first diffraction grating and the second grating is substantially transparent for a wave length possessed by a laser beam source whose beam is diffracted by the first diffraction grating, of the first and second laser beam sources and diffracts a wave length possessed by a laser beam source whose beam substantially passes through the first diffraction grating, of the first and second laser beam sources; and the wave length plate provides a wave length of emission light which substantially is transmitted through the first diffraction grating with a phase difference of xc2xc wave length.
According to the present invention, a light emitted from the first laser beam source, having the first wave length and linearly polarized light is diffracted by the second diffraction grating. Its 0-order diffracted light substantially is transmitted through the first diffraction grating, further transmitted through the wave length plate and is introduced toward the information recording medium. A reflected light from the information recording medium substantially is transmitted through the wave length plate and further is transmitted through the first diffraction grating and this light is diffracted by the second diffraction grating and its xc2x1primary-order diffracted light is irradiated to the light receiving device substrate. A light emitted from the second laser beam source, having the second wave length and a linearly polarized light substantially the same as that of the first laser beam source passes through the second diffraction grating. This transmitting light is transmitted through the first diffraction grating and is provided with a phase difference of xc2xc wave length . The light whose phase is changed is introduced toward the recording medium. A reflected light from the information recording medium is further provided with a phase difference of xc2xc wave length by the wave length plate so as to be changed to a linearly polarized light perpendicular to that of the incident light. This light is diffracted by the first diffraction grating in a polarized state and its xc2x1primary-order diffracted light substantially is transmitted through the second diffraction grating and then is irradiated to the light receiving device substrate. Consequently, when an emission light from any one of the first laser beam source and the second laser beam source passes through any one of the first and second diffraction gratings, they substantially are transmitted therethrough, and only when they pass through the other, they are diffracted. Consequently, light usability in a process from any one of the first and second laser beam sources up to the light receiving device substrate is substantially the same as an conventional example. Further, when an emission light from the other one of the first laser beam source and second laser beam source is introduced to the information recording medium, it substantially is transmitted through both the first and second diffraction gratings. Then, the light is diffracted by one of the first and second diffraction gratings first after it is reflected by the information recording medium to return to the light receiving device substrate. Consequently, light usability in a process from the other one of the first and second laser beam sources up to the light receiving device substrate is far more excellent than a conventional example. Further, because it is so constructed that the first laser beam source and second laser beam source are disposed in the vicinity of each other, emission lights from the first laser beam source and second laser beam source are emitted to the information recording medium along substantially the same optical axis and the reflected lights are returned along substantially the same optical axis as the former optical axis, the first laser beam source/second laser beam source and the light receiving device substrate can be disposed in the vicinity of each other, so that a compact optical pickup can be constructed.
To achieve the above object, according to a fourth aspect of the present invention, there is provided an optical device for use in the optical pickup described in the first aspect wherein the first laser beam source, the second laser beam source, the first diffraction grating, the second diffraction grating and the light receiving device substrate are integrally fixed in the same casing.
The optical device according to the fourth aspect of the invention is capable of obtaining the same effect as the optical pickup described in the first aspect.
To achieve the above object, according to a fifth aspect of the present invention, there is provided an optical device for use in the optical pickup described in the second aspect wherein the first laser beam source, the second laser beam source, the first diffraction grating, the second diffraction grating and the light receiving device substrate are integrally fixed in the same casing.
The optical pickup according to the fifth aspect of the invention is capable of obtaining the same effect as the optical pickup described in the second aspect.
To achieve the above object, according to a sixth aspect of the present invention, there is provided an optical device for use in the optical pickup described in the third aspect wherein the first laser beam source, the second laser beam source, the wave length plate, the first diffraction grating, the second diffraction grating and the light receiving device substrate are integrally fixed in the same casing.
The optical device according to the sixth aspect of the present invention is capable of obtaining the same effect as the optical pickup of the second aspect.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.